Residual nitrite plotted against incubation time for experiments in which homogenates of sanguinous (A) or asanguinous (B) heart tissue were incubated with 2,000 nmol/l sodium nitrite at 25°C under conditions listed. Oxy, incubation medium purged with oxygen; De-Oxy, purged with nitrogen; De-Oxy pH 5.5, pH of medium adjusted to 5.5 with HCl and then purged with nitrogen; De-Oxy allo, pH of medium adjusted to 5.5 with HCl and then purged with nitrogen in presence of 100 μM allopurinol. *P < 0.05 vs. time = 0.